Nitrogen oxides and other pollutants here include nitrogen oxides (NOx), photochemical oxidants, and ozones. Among the nitrogen oxides, nitric oxide and nitrogen dioxide are especially important in their effects on human beings and their environment. Nitric oxide (NO) is generated from so-called fixed sources such as steam-power plants and furnace operations and from so-called moving sources such as automobiles. Nitrogen oxides are also released directly into the atmosphere from such things as the nitrification process in the chemical industry. Nitrogen oxides lead to the regional and local atmospheric pollutions. The atmospheric pollution due to nitrogen oxides in Japan has rapidly worsened in the past ten years. The knowledge we have today on the effects on human beings is mainly on nitrogen dioxide; the knowledge on nitric oxide is still insufficient. Therefore, the authors are recommending environmental standards for nitrogen dioxide. The authors define photochemical oxidants as oxidizing substances, exclusive of nitrogen dioxide, which are generated by the photochemical reaction. This is based on the method of measurement, using neutral potassium iodide solution, which will be mentioned later. It has been confirmed that, in this case, most of the measured values are due to ozone. The authors recommend the environmental standards of photochemical oxidants as an index of photochemical-reaction-generated pollutants.